Laundered amorphous reinforcing lignin

ABSTRACT

Lignin of improved reinforcing properties in polymers, is prepared by steps comprising: A. LAUNDERING CRUDE LIGNIN IN AN AQUEOUS MEDIUM UNTIL SUBSTANTIAL AMOUNTS OF NON-LIGNIN MATERIAL ARE SOLUBILIZED AND SEPARATED, B. REFORMING THE LIGNIN BY ONE OF (I) PRECIPITATING WITH ACID AT A PH of about 2 to about 3 at a temperature of about 88* to 95*C; and (ii) conditioning wet lignin precipitate at said pH and said temperature, and C. WASHING THE PRECIPITATE TO REMOVE SOLUBLE MATERIAL AND DRYING THE RESULTING SOLIDS. Laundering additives have been used in step (a), and impurity dispersants in step (b). Polymer latices can be added before precipitation (b) and the lignin-latex coprecipitated. The lignin can be milled directly into rubber to give ultimate tensile strengths at least of the order of 2,800 p.s.i. This lignin can also be used as a reactive reinforcing filler in plastics.

i United States Patent 191 Sirianni et al.

[ LAUNDERED AMORPHOUS REINFORCING LIGNIN [75] Inventors: Aurelio F. Slrianni; Ira E.

Puddington, both of Ottawa, Ontario, Canada Canadian Patents and Development Limited, Ottawa, Ontario, Canada [22 Filed: Apr. 19,1972

211 App]. No.: 245,356

[73] Assignee:

[52] US. Cl...... 260/124 R, 260/124 A, 260/124 B, 260/124 C, 260/l7.5

51 1m. (:1 C07g 1/00 [58] Field of Search 260/124 R, 124 B, 124 C, 260/124 A [56] References Cited UNITED STATES PATENTS 2,949,448 8/1960 Toppel 260/124 R 3,167,523 l/l965 Dimitri..... 260/124 R 3,296,158 I/I967 Dimitri 260/124 R FOREIGN PATENTS OR APPLICATIONS 188,966 2/1964 U.S.S.R 260/124 R [45] June 18, 1974 Primary ExaminerLewis Gotts Assistant ExaminerD. R. Phillips Attorney, Agent,'0r FirmAlan A. Thomson [57] ABSTRACT Lignin of improved reinforcing properties in polymers, is prepared by steps comprising:

a. laundering crude lignin in an aqueous medium until substantial amounts of non-lignin material are solubilized and separated,

b. reforming the lignin by one of (i) precipitating with acid at a pH of about 2 to about 3 at a temperature of about 88 to 95C; and (ii) conditioning wet lignin precipitate at said pH and said temperature, and

c. washing the precipitate to remove soluble material and drying the resulting solids.

Laundering additives have been used in step (a), and impurity dispersants in step (b). Polymer latices can be added before precipitation (b) and the lignin-latex coprecipitated. The lignin can be milled directly into rubber to give ultimate tensile strengths at least of the order of 2,800 psi. This lignin can also be used as a reactive reinforcing filler in plastics.

11 Claims, 1 Drawing Figure PRECIPITATION TEMP c TENSILE STRENGTH p si l l l SURFACE AREA M lq PATENTEB JUN l 8 I974 TENSILE STRENGTH p s i PRECIPITATION TEMP C so so SURFACE AREA M LAUNDERED AMORPHOUS REINFORCING LlGNIN This invention provides a method for the preparation of very amorphous lignin products of high purity from crude lignin materials of industrial origin, and including the lignins separated from residual wood pulp liquors (particularly the black liquors). The purified lignin products prepared by this method impart reinforcement to styrene-butadiene rubber (SBR) and other analogous natural and synthetic rubbers at least as good as obtained with present lignin-latex coprecipitates. The tensile strengths attained for the vulcanizates compare favorably with the reinforcing carbon black containing rubbers.

it is well known that lignin obtained from the waste black liquors, coprecipitated with styrene-butadiene rubber-(SBR) latex, imparted very desirable physical properties to the vulcanizate. In comparison to carbon black, it is less dense, non-conducting, and being lighter in color, it appears more amenable for the preparation of light-colored rubber compounds. Difficulties have been encountered in filtration, and a twostep heat treatment was necessary to get acceptable filtering rates for the coprecipitate. Slow drying of the ligninrubber crumb rendered masterbatch production unattractive economically. Transportation cost of either latex or blacl-t liquor was another deterrent to the wide-spread use of coprecipitate. Thus, the one disadvantage to the wide spread use of lignin as a reinforcing agent for rubber is the necessity of coprecipitating it with the rubber from the latex," (lndia Rubber World Vol. 124 page l78 May 1951 by J. J. Keilen, W. K. Dougherty and W. R. Cook).

Early attempts to mill dry lignin intoSBR masterbatch were unsuccessful. It was felt for a long time that no lignin of any type will reinforce if it is added as a dry powder and milled with rubber, (Canadian Chemical Processing, Vol. 43 April 1959 page 37). Dry lignin milled into rubber shows almost no reinforcing effect. This is believed to be a result of the lignin particles adhering together by hydrogen bonding and thus not being dispersed into the rubber by milling" (see 0. W. Burke Jr. in Reinforcement of Elastomers, edited by Gerard Krause. lnterscience Publishers, copyright (1965) p. 506).

The adherence of the lignin particles together on milling is possibly owing to several unforeseen factors;

a. Condensation of the lignin particles if subjected to too high a temperature (before or after precipitation),

b. Precipitation of the sodium lignate at a temperature at which clusters oflignin, although very finely divided,.can close-pack in aqueous suspension and adhere strongly together on drying, and

c. The presence of a non-lignin constituent orperhaps a low molecular weight fraction in the isolated crude lignin. This constituent could prevent the lignin from dispersing into the SBR on milling by acting an agglomeratin g or coupling agent, and promoting clustering of the lignin particles rather than their dispersion.

[t was found possible to remove detrimental material according to this invention and leave behind a product of a highly amorphous nature that was very suitable for reinforcing SBR. The desirable product was formed TABLE I Tens. Lignin Melt. Impurity Lignin Str. (psi) Temp. "C Globules Untreated lndulin AT '500 205 Copious lndulin AT 2300' 2IO Fewer lndulin AT 2800 2 l4 Very few lndulin AT 3100 22] None Treated similarly to Example I below, but to give progressively increased laundering.

The non-lignin portion of the crude commercial product is not completely separated by merely dissolving the lignin in alkali and regenerating it in the acid form by precipitation with a mineral acid in the usual fashion. We have now found that a preliminary extraction, leaching or laundering is required to remove non-lignin materials which are detrimental.

According to the invention a purified lignin product has been prepared which, when cold milled into rubber formulations over a prolonged period of time, showsno enlargement or agglomeration of the lignin particles which would lead to lower tensile strengths of the vulcanizate. The method involves preparation of waterinsoluble lignin from crude lignin in which watersoluble, or water-dispersible impurities, or constituents, are separated from the crude material without degrading substantially the reinforcing constituent of the lignin (followed by a final precipitation or conditioning at critical temperature and pH).

The process includes the optional use of watersoluble polar organic emulsifiers such as acetone, lower alkanols (e.g., methanol, propanol), triethanolamine, and the like, or bicarbonates (e.g., NaHCO KHCOQ as an aid in the removal of water-soluble, or waterdispersible portions of the crude lignin during the laundering step. These agents are added to the aqueous lignin suspension, and are believed to act as wetting agents or emulsifiers for impurities. Salts such as sodium chloride or sodium sulfate may be used to minimize ldaching or poor filtering of the lignin itself. A preferred variation of the laundering or soaking is the pH adjustment of the crude lignin suspension to below about pH 6, prefera bly to about pH 2.5, using an acid such as hydrochloric, phosphoric, formic, acetic and the like, but preferably sulfuric, and allowing the system to soak desirably for at least 2 1/2 hours.

The most critical step in the process is the final lignin precipitation (or conditioning of the final wet precipitate before drying). The highly amorphous lignin of improved reinforcing properties was found to be obtained only when the reconstitution or reformation took place at from about 88-95C and at a pH of about 2 to 3. Preferably the following separation or filtration should be at this temperature. Both the upper and lower temperature limit was important but may vary slightly for different types of lignin or for lignins of different pro cess history. Substantially equivalent results were obtained at a pH of 2.5 -3 with close to 3 being preferred for reagent economy. If either the laundering or purification step or the controlled final precipitation, reformation or conditioning step is omitted, the improved reinforcement will not be obtained.

The method includes the optional use of alkaline salts such as sodium silicate, sodium borate or trisodium phosphate as dispersants for the impurities in the lignin during the final precipitation of the lignin.

Various types of lignins may be used in the preparation of the novel lignin products of improved reinforcing properties. Crude lignins from sulphite liquors, and modified lignosulphonates have been processed. A further aspect of this invention is the separation of novel lignin products from Spruce black liquors, and from various other Kraft black liquors using a stepwise pH adjustment before final conditioning at pH 2-3, in which the purified lignin product obtained has enhanced reinforcing properties.

The initial separation of lignin from black liquors preferably includes centrifuging off insolubles, heating the solution and lowering the pH until the lignin precipitates, cooling, filtering and washing the lignin precipitates. Desirably the lignin is initially recovered by heating the crude pulp liquor to about 8092C, centrifuging, reheating to said temperature and precipitating the lignin.

The use of liquid dispersing agents such as vinylic silanes, or fatty acid esters, has been found to aid in the more efficient milling of the novel lignin product into rubberv Unexpectedly it was found that improved reinforcing properties were still obtained if the final lignin precipitation was a coprecipitation with rubber latex. The same temperature and pH limitations were found necessary for the lignin-latex coprecipitation as for the final lignin precipitation or conditioning. An advantage in compounding was obtained if a mixture, slurry, wet cake. or paste of compounding additives was intimately mixed with the wet coprecipitate before drying (subsequent milling time was greatly reduced).

in the attached drawing, FIG. 1 is a graph showing the effects of the final precipitation or conditioning temperature. and the lignin surface area on vulcanizate tensile strength.

The lignin products were evaluated using the following recipe. In some cases it was prepared in sufficient quantity to be used as a masterbatch.

Parts by weight A Krxlenc I500 (Polymer Corp. Sarnia. 100

Out. trade name for an SBR rubber) PBNA (Phenyl-heta-naphthylaminel Litharge Altax (trademark for henzothiazyl disulfitlel Cumate (trademark for Cu dimcthyldithioearbamate) Stearic acid Sulfur Masterbatch A enough for 25-30 individual tests Milling of Lignin into Masterbatch Portions of about 1 14 g. of the rubber masterbatch were milled and blended on a 12 inch open mill with the following ingredients:

Parts by weight B Silane A174 (gammamethacryloxypropyl 2 trimethoxysilane-Union Carbide Corp.) Lignin 40 C' cosol ZXH (or 42 40 processing 5 oil Sun Oil Co.) Zinc Oxide 5 The rubber masterbatch was sheeted, and the silane was dispersed into it by milling. Then followed the addition of 40 g. lignin, the oil and finally the zinc oxide. The system was milled for approximately 10 minutes. The approximate time of cure at 275F was obtained by means of a Shawbury Curometer, (H. W. Wallace and Co. Ltd. The sample was then passed through the mill 6 times, and an g. portion was cured at 275F for this time under 1,500 psi pressure. The cured specimen was chilled under water, stored at room temperature for 1 hour or longer, then tested for tensile strength as per A.S.T.M. No. D4l2-68.

Lignin from a number of sources was used in illustrating this invention. lndulin AT was obtained in 50 pound bags from Westvaco Chemical Products, Charleston, W. Va:, U.S.A. Its specification is as follows:

Moisture 67! Packed apparent density 25 lh/cu ft.

Surface area (average 3.49'sq. meters/gram] Methoxyl content 13.9%

Sulfur 1.4%

Sintering point 4l(lF( 2l()C) Additionally, lignin known as Tomlinite" was obtained from Domtar Research Ltd., Senneville, Quebec, and a heat-modified Kraft lignin from Industrial Cellulose Research (C.l.P.) Hawkesbury, Ontario. Spruce Kraft black liquor containing about 10 percent by weight of lignin, obtained from Domtar Research Ltd., and Kraft black liquor and a heat modified Kraft black liquor each containing about 5 percent lignin obtained from C.l.P. Hawkesbury; were also employed. A sample of an oxidized desulphonated lignosulfonate insoluble under acid conditions obtained from the Ontario Pulp and Paper Co., Thorold, Ontario, was also used as a raw material for illustrating this invention.

These lignins of industrial origin including lndulin AT and Tomlinite"; and the experimental types including the heat-modified dry Kraft lignin contained unspecified amounts of a material. seemingly nonlignin in nature, as an impurity. It is probable that this impurity consists of small amounts of resins, waxes, esters, acids. polysaccharides, and other organics including some alkali-insolubles which are not completely separated after acidification of the liquors.

In the case of lndulin AT, the color of the lignin and the pH in agueous suspension usually varied from bag to bag. lndulin AT appeared to fall, for the purpose of treatment by this invention, into several groups. Group A lndulin AT having pHs which range up to about pH 6, when 50 to 200 g. lignin are soaked or dispersed in 2 3 l. of water overnight. These lignins were thermally stable, in that, it was possible to heat the lignin in aqueous suspensions up to a temperature of 95C. in order to remove water-soluble or-dispersible impurities according to the invention. Group B lndulin AT having a pH greater than 6 after the soaking in water. l. stability was poor owing to high solubility in hot water. The lignin shrank badly when precipitated in the same fashion as the group A lignins. l. I. Group C lndulin AT having a pH greater than 6 after the soaking in water. It contained a larger quantity of waterextractable material than the lignins from Group A or Group B. On precipitation it behaved similarly to Group A lndulin AT.

It was discovered that all of these crude lignins produce excellent reinforcement after the purification pretreatment and final precipitation or conditioning. The steps involved comprise:

a a. laundering crude lignin in an aqueous medium until substantial amounts of non-lignin material are solubilized and separated,

b. reforming the lignin by one of (i) precipitating with acid at a pH of about 2 to about 3 at a temperature of about 88 to 95C; and (ii) conditioning wet lignin precipitate at said pH and said temperature. and

c. washing the precipitate to remove soluble material and drying the resulting solids.

The following Examples illustrate various aspects of the invention.

EXAMPLE I Samples of 60 and 200 g. lndulin AT were soaked in 3 l. of water at room temperature. The pH of the lignin suspensions was adjusted below about pH 6 preferably to pH 2.5, with acid. The suspensions were allowed to soak, leach or launder at room temperature overnight,

while hot. The g. quantities were heated in about 3.5

l. of water, while the 200 g. lots were heated in about 8 l. of water. The filter cake was rinsed with warm water until the filtrate was clear in each case, and again dispersed in fresh water. While stirring and heating, the lignin was dissolved with 10 percent sodium hydroxide based on the original weight of the lignin, then precipitated at a specific temperature with sulfuric or hydrochloric acid by reducing the pH from about ll to pH 3 2.5. The 60 g. lots were precipitated while stirring in 3.5 l. of water with the 200 g. lots in about 8 l2 l. of water. The lignin suspension was filtered immediately after precipitation and the filter cake rinsed with warm water to remove excess salts. The filter cake, the pH of which rises quickly to about pH 4 following the water rinsing step, was dried at about 130 to [F in a forced air oven.

Although'the lignin could be washed after the .soaking step at up to about C. without anydeleterious effects, purified lignin products possessing .good reinforcing properties were obtained only if the precipitation step was carried out between about 88- 95C i( see Ex. 2). The non-sticky precipitate filtered easily and dried quickly when the precipitation was carried out over this narrow temperature range. About 80 87 percent of the original weight of the lignin was recovered in a highly amorphous 'fonn (according to X-ray diffraction measurements) containing less than 1 percent moisture. The high amorphicity of the lignin decreased sharply when the precipitations were done outside of this temperature range (88 95C.).

EXAMPLE 2 Effect of the final precipitation temperature on the tensile strength of the vulcanizate A marked increase in the reinforcing properties of lignin was observed after the isolated lignin was laundered, dissolved with alkali, then precipitated with a mineral acid preferably at about 92C. from about pH l 1 down to about pH 3.

The following Example illustrates that amorphous lignin products possessing desirable reinforcing properties were obtained when the precipitations were carried out over a temperature range between about 88 to 95C. As shown in Table 11 and in FIG. 1, decreases in tensile strength occurred outside this temperature range. Precipitates formed below 88 to 89C. appeared to be feathery and dried to a rather compact form with a higher surface area. The filtration rate decreased with decreasing precipitation temperature. Lignin products obtained by precipitation above about 95C. also showed lower reinforcing properties (the filtering rate is high however). The decrease in reinforcing properties is possibly owing to the irreversible condensation or shrinkage of lignin particles. Between 88- 95C.. both the filtration and drying of the filter cake is rapid. Suspensions containing 200 g. lignin in about l0 12 l. of water filtered in less than 4 minutes under vacuum, using a 33 cm. dia. creped filter paper. The lignin dried -to an amorphous product even at room temperature, A smear of the filter cake dried to a fine powder within several minuted without checking or distortion. This possibly signifies that a lignin aerogel type of product was produced.

Although the possibility of precipitating the lignin solution at a lower temperature, then heating the wet precipitate upto the critical temperature range of 88- 95C. is not excluded, the product obtained under these conditions does not TABLE II Effect of Precipitation Temperature (P. Temp.) on Tep' sile Streggth of SBR Vplcagizatg "C M lg Cure Time Modulus at T, (psi) E H Additive during P. Temp. Surface Area Min. 300% Precipitation 70 l0 65 870 36 with sodium silicate 85 60.6 30 300 360 4l0 53 no sodium silicate 86 62.5 20 3I() 400 440 55 with sodium silicate 88.5 59.4 25 425 I825 770 56 y 'do. 60-9l' 27 420 2500 790 56 do. 92-9l 48.5 33 425 2925 790 60 do.

TABLETI Continued tive during "C M g Cure Timc Modulus at E H Addi P. Temp. Surface Area Min. 300% Precipitation 90 25 420 2760 830 58 no sodium silicate 90 30 450 2900 770 58 with sodium silicate Ell-92 30 450 3000 830 58 do.

9l-92'" 25 440 3000 830 57 do.

9l-92"' 30 480 3250 770 58 do.

92 48.7 33 425 3l50 BIO 60 do.

92 36.9 33 450 2800 790 56 no sodium silicate 94 30 385 30l0 800 59 with Borax 95 34.2 25 400 2575 760 59 with sodium silicate 98 22.9 30 400 2250 8l0 55 do.

85-96" 25 400 2325 840 55 no sodium silicate I 10.3 30 340 i410 790 50 with Sodium silicate Note:

' The sodium lignate was precipitated at 60C then heated up to 9lC and filtered immediately The sodium lignate was precipitated at 85C then heated up to 96C and filtered immediately In lieu of silanc. methyl dichlorostearate was used in milling 1' l3 Tensile strength at break E, l3 Elongation at break ('1) H Shore "A" hardness appear to be quite as good a reinforcing material: While the reason for this is not too clear, it is probably owing to occlusion of impurities, or perhaps to the close packing of lignin particles during the desolvation step, or over-riping owing to the longer heating cycle.

EXAMPLE 3 A series of experiments was carried out with lndulin AT from group A in order to show the effect of the water washing temperature (W.W.T.) of the raw lignin and precipitation temperature on the tensile strength (T of the vulcanizate. About 200 g. of lignin were- TABLE lll Physical Properties of Vulcanizatcs Using Lignin Precipitated in the Presence of Alkaline Salts Salt Cure Time Modulus at T,, (psi) E H "C Prccip.

Min. 300% W.W.T. Temp.C Used 25 390 2875 8 IO 60 92 92 Na Silicate 25 450 2940 750 6] 92 92 do. 385 30l0 800 59 92 94 Borax 440 2875 760 '59 Borax 30 450 2750 770 6| 92 92 Na, P0

EXAMPLE 5 soaked at room temperature in 3 l. of water for 3 days. After filtration, the lignin was dissolved in alkali sufficient to give a pH of about ll, and the temperature raised to 92C. The lignin solution was precipitated quickly with a suitable quantity of dilute hydrochloric acid (the pH of the system was reduced from about 1 l to pH 2.5 3.0 at 92C). Tensile strengths were found to increase slightly with increasing laundering temperatures. reaching a maximum at about 92C. then decreasing above 95C. Some irreversible "degradation" of the lignin was indicated when the lignin suspension was heated in water above about 95C.

EXAMPLE 4 V alkaline salts are added to the lignin suspension with Group B, lndulin AT had pH values greater than 6 when 200 g. of the-raw material was soaked in about 3 l. of water at room temperature. The supernatant liquid after soaking and the filtrate from the water washing treatment was much darker than from the lignin samples having a pH less than 6. However, the reprecipitated lignin product obtained was not much better than untreated material. Some improvement occurred by processing this lignin under standard conditions with a blanket of nitrogen. The reason for the low tensile strengths observed for the vulcanizates containing lignin from Group B is probably due to fractionation and/or degradation of the lignin. Samples treated under identical conditions without the water soaking step were slightly better, provided the pH was lowered below 6 in the water washing step. However very amorphous lignin was produced by acidifying the aqueous crude lignin (Group B) suspensions during the soaking operation to a pH below 6, then following the precedure developed for Group A lignins. An illustration of the method employed to accommodate Group B lignin is as follows:

due was dispersed in fresh water in a 4 l. beaker, and 10 while stirring was heated under nitrogen up to about original lignin was recovered in an amorphous purified state. The physicalproperties obtained'for the vulcanizate and the surface area of the-lignin used are summarized in Table V. Surface Areas were measured by nitrogen adsorption using a Strohlein Area Meter. The pH during soaking or laundering was 2-3 in all cases.

TABLE V Physical Properties of SBR Vulcanizatcs and Surface Areas of Lignins Used Sulfuric acid used to precipitate the lignin solution. The lignin solution was precipitated in the absence of sodium silicate.

' lignin was soaked for about 3 weeks in 3 l. of water 666 taining l2 ml. 20 percent H 80 The supernatant liquid at about pH 2 3 was decanted. The residue was heated in 10 l. of water under nitrogen up to about 60C and filtered. The filter cake was rinsed with warm water until the filtrate was virtually clear. Following this, the filter cake was dispersed in 8 l. of water at about 50 60C., and the lignin dissolved with a solution containing 20 g. sodium hydroxide and 32 g. sodium silicate. The solution was heated while stirring and precipitated with dilute hydrochloric acid by reducing the pH from 1 l to about 3.0 at 92 93C. The suspension filtered within 4 minutes under suction, using a 33 cm. dia. creped filter paper. The filter cake was rinsed with 4 washes of 3 1. each of warm water and 2 rinses of 800 ml. distilled water. The final pH of the filter cake after the removal of excess salts rose quickly to pH 4 or over. About 85 percent by weight of the 6190C. (W.W.T.). The suspension was filtered imas? gfllgf H ';j, mediately. The filter cake was rinsed under suction with about 2 l. of warm water. The filter cake was dis- 30 400 o 35 490 3010 760 62 48.3 persed 1n 3 l. of fresh water at 30 C. and the lignm d1s- 30 385 2950 850 57 51M solved with a sodium hydroxide solution containing 6 33 2 800 59 50.1 g. alkali and 8 g. sodium silicateuThe solution was g 28 2:; heated with steam and under nitrogen. While stirring 30' 450 2900 830 58 515* the solution was precipitated with dilute hydrochloric N I J S d, r l I T n d 'hdll If g I u 92C. l l 2.9' mop; gi l-gm ignalc SO UUUn db "1.! )PrCClplI-IIL ll IUlL hU UIIL JLI precipitate was filtered immediately. The filter cake v was rinsed 4 times with l l. of warm water each time. Lignin products which reinforced SBR to at least The lignin products dried to less than 1 percentmois- 2,900 psi were obtained from all bags of lndulin AT ture at 130F. overnight. and from other raw Kraft dry lignins by the method just Relationship found between the pH in which the lig- 25 described. nin was soaked and tensile strength of the vulcanizates is shown in Table IV. EXAMPLE 7 Modified Lignin Soaking Treatment EXAMPLE 6 Desirable amorphous reinforcing lignin products Other bags of lndulin AT from Group B behaved in 30 were also obtained from lndulin AT when small quantithe same fashion. For example, a number of experities of acetone, methanol, triethanolamine, or sodium ments were conducted using 200 g. lignin batches from bicarbonate were used with the lignin in the soaking other bags. The raw treatment.

TABLE IV Ph sical r0 1 sofvulc ,1 'on ii i 1' pH W.W.T k Lignin Surface Area Time ofCure Modulus T, EB .H Soaking C recov. Mlg in. 300% 7.8 (Natural) 90.5 80 67 30 300 450 530 55 NO soaking (control) 86 (pH 3.6) 78.3 300 1250 830 53 6.0 86 85.7 365 1875 790 54 5.3 25 86.8 380 2870 830 56 3.8 86 87.0 30 450 2900 770 58 3.2 86 86.6 30 340 2950 870 54 1.9 86 85.0 36.9 30 345 2850 850 54* 1.9 61 85 48.3 30 440 3170 s20 59 As an illustration of this technique, about 200 g. lndulin AT from Group C were soaked in 3 l. of water at room temperature overnight. The lignin suspension was adjusted from about pH 7.5 down to pH 2.5 with sulfuric acid. The and the filter cake was was agitated in the presence of ml. acetone for 2 hours, then filtered. The filter cake was rinsed with water at C. The residue was dissolved with sodium hydroxide in the presence of sodium silicate. The solution was precipitated at 92C. with dilute hydrochloric acid in the usual fashion. A similar illustration was provided by using 25 ml. methanol in lieu of acetone. Another illustration'of this method was carried out using 200 g. lndulin AT from Group A in which 5 ml. triethanolamine were added to the suspension in lieu of acetone or methanol.

Another illustration is provided as follows: About 200 g. lndulin AT from Group B were soaked in 3.5 l. of water containing 2 g. sodium bicarbonate, overnight.

TABLE VI Physical Properties of SBR Vulcanizatcs Filled with EXAMPLE 11 Effect of Milling Time on the Physical Properties of the Vulcanizates The amorphous lignin products produced by this method possess remarkable stability. These products can be milled with SBR without the lignin particles clustering together in the rubber. This indicates that impurities believed responsible for the adherence of Lignin Products Obtained From Modified Soaking Procedgrc Cure imc odulus at T,, (psi) E, H Laundering Additive Min. 300% 30 450 2925 790 58 Acetone 30 390 2 700 8 I 56 Methanol 30 375 2960 850 56 Triethanolamine 30' 400 2885 800 57 Sodium Bircarbonatc Note: No sodium silicate used EXAMPLE 8 A Kraft modified lignin obtained from C.l.P. Hawkesbury was soaked in Water, filtered hot (90C), washed, redispersed in water and dissolved by sodium hydroxide sodium silicate addition. The solution was heated and the lignin precipitated with acid from pH 1 l down to pH 2.8 at 93C, filtered and the precipitate washed and dried. About 82 percent of the'original weight of the lignin was recovered in a very amorphous form which had similar reinforcing properties to lndulin AT treated according to the invention.

EXAMPLE 9 A crude lignin designated Tomlinite" (obtained from Domtar Research Ltd.) was treated as above similarly to lndulin AT from Group A. The properties of the vulcanizate containing this treated lignin were similar to those of vulcanizate reinforced with the treated lndulin AT.

EXAMPLE 10' illustrative example using a desulphonated lignosulphonate lignin in the form of the sodium salt obtained from the Ontario Paper Co.

About l00 g. of this crude lignin were laundered as above for Group B lndulin AT (see Example The filter cake was dispersed in 3.] of water and the lignin dissolved while heating in the presence of g. NaOH and 16 g. N grade sodium silicate. The solution was precipitated while stirring with dilute hydrochloric acid by decreasing the pH from about I 1 down to pH 2.9 to 92C. The suspension was filtered immediately and the filter cake rinsed with warm water to wash ofi excess salts. The filter cake was dried at l80F in a forced air oven overnight. The vulcanizate results obtained are:

Further curing was not attempted.

the lignin particles together are removed by the water washing or laundering step.

As an illustration, about 436 g. of the standard masterbatch was milled with 8 g. silane A174, 160 g. lignin and 40 g. Circosol 4240. As the material was being milled, 4 aliquot quantities of the mixture were removed after 15, 25, 40 and minute millings. Each sample removed was milled for a further 5 minute period with 5 g. zinc oxide. The rubber sample was sheeted and an g. sample was cured for 30 minutes at 275F. The tensile strength attained for the vulcanizate as a function of milling time is summarized in Table Vlll.

This invention includes the separation from various black liquors of the lignin in a dry highly amorphous form possessing very desirable reinforcing properties for SBR or other rubbers. The lignin can be separated from the black liquor by acidification with a mineral acid. If the black liquor is treated with CO or carbonic acid, the lignin is precipitated in the form of a salt at about pH 9-10. After the addition of a small quantity of a salt such as sodium chloride or sodium sulfate to the black liquor, non-lignin material soluble in the alkaline media is removed on filtration. The lignin is sufficiently salted out that filteming of the suspension occurs at a reasonable rate without blinding the filter. The filter cake is rinsed with cold water, then suspended in water and the lignin precipitated at to C. with a mineral acid to about pH 4. The lignin is filtered and rinsed with hot water. The filter cake is redispersed in water and the pH of the suspension adjusted to about pH 3 for final conditioning at about 92C. The lignin product is then filtered, washed with warm water to remove excess salts, and dried.

illustrative example in which Domtar Spruce black liquor is centrifuged then precipitated with CO About 3,700 ml. Spruce black liquor were heated up to 99C. while stirring in the presence of g. sodium chloride. After cooling to room temperature the black liquor was diluted with 800 ml water. The solution was centrifuged in order to separate out insolubles. The centrifuged liquid fraction was heated up to 88C. then CO bubbled through the solution while cooling to room temperature. The precipitate (at about pH 9.4) was filtered at room temperature. The filter cake was rinsed with cold water.

An aliquot portion of the filter cake was dispersed in about 8 l. of water containing g. sodium silicate. The lignin dispersion was heated up to 85C., and the lignin was precipitated by acidification to about pH 4.1 using,

10 percent sulfuric acid. The suspension was filtered immediately and the filter cake rinsed with warm water. The rinsed filter cake was redispersed in about'8 l. of water and heated while stirring under nitrogen up to 86C., filtered and rinsed with warm water until the filtrate was clear. The lignin was again dispersed in 8 l. of fresh water, heated up to 92C. and the pH adjusted from about pH 5.0 down to pH 2.9 with dilute hydrochloric acid. The suspension was filtered immediately and rinsed with warm water. The washed filter cake, at about pH 4.5, was dried at 130F. overnight. As an illustration a similar example was prepared in the same fashion in the absence of sodium silicate.

The physical properties of the vulcanizates forced with these products were:

reinl4 8 TABLE X EXAMPLE 14 heated up to 88C; then while cooling CO was bubbledv through the system in order to precipitate the lignin. The suspension at pH 9.6 was filtered, then rinsed with a small quantity of cold water. The filter cake was dispersed in about 8 l. of water containing 32 g. sodium silicate. This lignin solution or dispersion was heated up to 82C. then acidified with 10 percent sulfuric acid to about pH 4. The suspension was filtered immediately. After rinsing with warm water, the filter cake at about pH 4.7 was redispersed in fresh water, heated up to 90C. and filtered. This treatment removed additional coloring matter from the lignin.

The filter cake was dispersed again in 8 l. of water,

heated up to 92C. under nitrogen and the suspension was adjusted to about pH 3 with dilute hydrochloric A series of experiments were done with lndulin AT from the same bag in which the water washing and precipitation temperatures were held constant at about 92C. The pH of the suspension .in the final acidification of the lignin solution was varied.

About g. crude lignin were soaked in -3 l. of water for about 20 hours. the lignin filtered and the residue heated in 3 l. of fresh water up'to 92C. The lignin was filtered immediately, and rinsed under suction with warm water. The filter cake was dispersed in 3 l. of water and the lignin dissolved with 5 g. NaOH. The sodium lignate solutions were precipitated at 92C to pH values ranging from about 1.8 to about 4. After rinsing the filter cake substantially free of salts, the lignin was dried at about lF for about 20 hours. The maximum tensiles were observed where the lignin solutions were acidified to pH 2.7 to 3.0 at 92C.

By setting the tensile strength at percent for the acid. The suspension was filteredimmediately. The pH of the filter cake increased to about 4.5 after rinsing with warm water. The filter cake was then dried to less than 1 percent moisture in a forced air oven at F. overnight (No. l).

Another example was carried out on CIP Modified Kraft black liquor in which the lignin product was obtained by the same stepwise reduction in pH but solignin prepared at pH 2.7 to 3.0, the tensile strengths 65 of the vulcanizates reinforced with lignin prepared at other pH values are shown below as a percentage of this figure;

dium silicate was omitted (Nos. 2 and 3).

The SBR vulcanizate reinforced with these lignin products had the following physical properties.

formed by acidifying a suspension of sodium lignate and rubber latex. The suspension is then heated up to an elevated temperature to coagulate the precipitate and improve the filtering rate. The system still contains a colloidal suspension which retards the filterning rate. The filtrate is frequently muddy and the filter cake remains sticky thus impeding the washing and the subsequent drying of the filter cake. We have discovered that the filtering, and drying rates of lignin-latex coprecipitates, without the appearance of muddy filtrates, are greatly improved by laundering and conditioning the lignin as described above. After the laundering treatment and controlled coprecipitation, the filtrate is clear, indicating losses of rubber and of lignin through the filter, manifested by the appearance of muddy filtrates, are eliminated. Illustrations of this aspect of the invention are given in Examples 15-17.

EXAMPLE 15 About 200 g. lndulin AT from group C was soaked in water for about 1 hr. The suspension was adjusted to pH 2.5 with sulfuric acid, allowed to soak for a further period of 3 hours, and filtered. The filter cake was dispersed in 8 l. of water. The dispersion was filtered under suction immediately after heating up to 90C, while stirring, in order to remove further quantities of water-soluble or-dispersible impurities. The filter cake was rinsed with 6 l. of warm water, dispersed in 4 l. of water, and while stirring the lignin was dissolved with a solution containing 20 g. NaOH and 16 g. N grade sodium silicate. About 750 ml. latex (20 percent rubber) was added and the system (diluted to about 101.) heated with steam up to 92C. While stirring the sodium lignate-latex solution was precipitated with dilute hydrochloric acid to pH 2.6. The lignin-latex coprecipitate containing about equal proportions of lignin to rubber in about 13.5 1. of water filtered under vacuum within 3 minutes at 9l92C using 33 cm. dia. creped filter paper. The filtrate was clear. The filter cake was rinsed with l 2 l. of warm water in order to remove soluble salts (this required about 10 minutes). The pH of the filter cake was about 4.4 after the rinsing step. The lignin-latex filter cake containing about 21 percent solids dried to less than 1 percent moisture at 140F overnight. A piece of filter cake about 2 cm. thick weighing about 25 g. dried at a rate of 3.6 g/hr. (weight loss) at 95C.

EXAMPLE 16 About 200 g. lndulin AT from Group C was soaked in 3 l. of water for 1 hour. The lignin suspension was treated as in Example 15, with the exception that the washing or laundering step was omitted. While stirring the lignin-latex solution was precipitated with dilute hy drochloric acid down to pH 3.0 at 92C. The 1:1 ligninrubber coprecipitate contained in 13.5 1. of water required 33 minutes to filter. The filtrated was Muddy.

16 It required 100 minutes of filtering time to rinse the filter cake with only 6 l. of warm water. A sample of filter cake about the same dimensions as in Ex. 15 dried at a rate of 3.0 g/hr. at 95 C.

An aliquot portion of the muddy filtrate was stored in a closed container. After about 2 months storage the disperse phase settled. It was filtered, washed free of salts then dried at 95C The loss of fine material through the filter was about 4 percent based on the weight of the dried lignin-latex coprecipitate product.

EXAMPLE 17 About 200 g. lndulin AT from group B were soaked for l 1 days in 3.5 l. of water adjusted with H 80 to pH 3.1. The supernatant liquid was decanted. The residue was dispersed in about 8 1. of water then heated while stirring up to 60C. The lignin suspension was filtered immediately under suction. The filter cake was rinsed with 6 l. of warm water.

The filter cake was dispersed in 4 l. of water at about 42C, and the lignin dissolved with a solution containing 20 g. NaOH and 20 g. N" grade sodium silicate. About 2,000 ml. latex were added (400 g. rubber) and the system while stirring was diluted with water to about 10 l. The system was precipitated with dilute hydrochloric acid down to pH of 3.0 at 92C. The suspension containing about 168 parts lignin filtered with a clear filtrate at a rate of 4.7 litres/min. The filter cake was washed with 12 l. of warm water in order to remove excess soluble salts. This required 10 minutes to filter.

The filter cake indicated a pH of 4.2 after the rinsing step. It was dried at 140F. Other similar runs were made as in Table Xll.

A comparison of the physical properties of the vulcanizat'es obtained with the laundered and unlaundered lignin samples are shown in Table Xll. In all cases the vulcanizates contained parts lignin per hundred of rubber (phr).

Lignin-latex coprecipitates showing excellent reinforcing properties for rubber were also obtained using the lignin in the form of the sodium salt separated from Kraft black liquor. The lignin-latex solution was coprecipitated in a stepwise reduction in pH without actually dissolving the lignin with alkali. Savings in time and chemicals are anticipated by this technique.

Acidification of any of the commercial black liquors from the alkaline pulping of wood will yield an alkali lignin containing variable amounts of alkali-insolubles as impurities. These impurities if sufficiently large lead to flaws in the vulcanizates. However, removal of the coarse insoluble particles is possible by centrifuging the black liquor before acidification, and further laundering is carried out during the coprecipitation.

This method for incorporating lignin from black liquor with rubber latex is illustrated in Examples 18-19.

TABLE X11 The behaviour and h s s i l I! 1 C Starting Ratio Lignin Filtering Washing Drying rate Cure tim 300% T (psi) E, H

Lignin: Rubber Group rate of Coppt. at 95C Min. Modulus 1002100 Group C 0.4 l/min 6 H100 min 3.0 g/hr 40 470 2820 780 61 640 2575 720 63 100:100 Group C m 4.5 l/min [0 H10 min 3.6 glhr 40 900 3500 670 72 100:100 Grou B m 4.8 llmin 40 500 3220 740 67 50 570 3400 710 67 501100 Group B 4.7 l/min l2 l/l0 min 40 675 3200 800 75' 720 3500 720 79 TABLE YTI Continued was filtered at room temperature under vacuum. Rosin acids, tall oils, etc., (if any present) remain in solution with the mother liquor (as the filtrate). Sodium chloride depressed the solubility of the sodium lignate, thus avoiding blinding of the filter paper. The filter cake was washed with a small volume of cold water to remove further quantities of water-soluble impurities en trapped with the filter cake. Hot water dissolves the sodium lignate leading to blinding of the filter paper and- /or loss of lignin product.

The lignin-rubber latex coprecipitate was prepared in the following fashion.

An aliquot portion of the sodium lignate filter cake containing circa 200 g. solidswas dispersedin about 8 l. of water containing 24 g. sodium silicate. About 1.200 ml rubber latex 18.2 percent rubber by weight) was added. The suspension was heated with stirring up to about 85C, then neutralized with a 10 percent sulfuric acid solution from about pH 10.3 to pH 3.9. The precipitate was filtered immediately under suction using a 33 cm. dia. creped filter paper. At this stage the filtering rate was about 0.75 l/min. The filtrate was very dark, but free from Muds. The blondish filter cake was rinsed with a liter of warm water in order to remove excess salts and colored matter. The filter cake was leached further by dispersing it in about 8 l. of water, heated up to 87C, and filtered again under suction. The filter cake was soaked in 8 l. of water overnight. It was then heated up to 92C, and finally acidified with lzl hydrochloric acid from about pH 6.1 to pH 3.0. The suspension was filtered under suction at about 92C. The filtering rate was now about 3.4 l./min The pH of the filter cake increased to about 4.9 after rinsing with warm water. The filter cake containing about 30.7 percent solids dried overnight to less than 1 percent moisture in a forced air oven at l40F. A 35 g. sample of filter cake about 2 cm. thick dried at a rate of 3.6 g/m at 95C. The lignin-rubber coprecipitate contained about 70 parts lignin phr. it had an apparent surface area of 6.2 Mlg.

The reinforcing capacity of this coprecipitate diluted to parts lignin phr with SBR was:

' l't x corcciitt S Drying rate 300% Starting Ratio Lignin Filtering Washing Cure time T tpsi) E Lignin: Rubber Group rate of Coppt. at C Min. Modulus 40x00 Group B m 3.2 l/min 10 l/l8 mii'i 40 475 '2950 850 68 60 580 3150 760 72 room Group C 3.7 g/hr 30 520 2950 740 so l The lignin was unlaundcred. (2) The lignin was laundered. (3) Filtralc was muddy. (4) Filtrale was clear.

EXAMPLE 1's 4 15 TABLE xm i Tim )fCu 300'; T E H About 4 l of Spruce black liquor containing about 10 1.375% n Modulus (ps i) H percent solids was heated with stirring up to 95C, .in the presence of 10 g. sodium chloride. After cooling to 20 60 670 3000 7 room temperature the black liquor was centirifuged in order to separate out insoluble matter. The clear liquor i was heated up to about 88C, and the lignin was precip- EXAMPLE l9 itated by passing CO through the system while cooling to room temperature. The suspension at about pH 9.4 25

A 4 l. portion of Spruce black liquor was treated as in example l8. An aliquot portion of the sodium lignate filter cake was dispersed in about 8 l. of water containing 20 g. N grade sodium silicate. About 1,000 ml. latex (18.2 percent solids) was added. The system was heated while stirring up to about 85C, then acidified with 10 percent sulfuric acid to pH 3.9. The suspension was filtered immediately under suction. The filtering rate was about 1.7 l/min; the filtrate was dark but clear. After rinsing the filter cake with warm water, it was dispersed in 8 l. of water, heated while stirring up to 9l-92C, and the pH adjusted with 1:1 hydrochloric acid from about 4.6 down to pH 3.0. The suspension was filtered immediately under suction. After rinsing the filter cake with warm water, the pH increased to 4.3. The filter cake containing parts lignin to 100 SBR dried to less than 1 percent moisture in a forced air oven at l47F.

The reinforcing capacity of the coprecipitate diluted with SBR to 40 parts lignin phr was:

TABLE XIV Time of Cure 300% T, E, H

at 275F Modulus (psi) 30 min. 485 2900 770 68 35 min. 550 3400 760 67 wet coprecipite filter cake more efficiently before drying. The mixing can be effected in either the slurry or paste condition i.e., the amount of water present is not critical. The subsequently dried lignin-latex coprecipitate containing the ingredients of the rubber recipe can then be molded directly, or if oil-extension is desired, this can be done on the mill with several minutes of milling time only. The vulcanizates obtained are more uniform in tensile strength.

EXAMPLE 20 "N" grade sodium silicate. About 1,885 ml. SBR rubber latex (circa 20 percent rubber by weight) was mixed with it, and the system steam-heated while stirring up to 92C. It was precipitated at 92C by acidification with dilute HCl from about pH 1 1 down to pH 3. The suspension was filtered immediately, and washed with warm water in order to remove excess salts.

'Litharge The following ingredients, (B),

PBNA 7 g.

were thoroughly mixed in a Waring blender in the presence of about 500 ml. water. The lignin-rubber coprecipitate containing circa 40 parts lignin phr and the ingredients (B) were thoroughly mixed in 8 l. of water at about 25C, and filtered again. The filter cake was dried at l40-160F in a forced air oven. This material can be molded under pressure with heat without milling. Also, it can be extended with oil on the mill as follows:

About 133 g. of the rubber composition fonned above was cold rolled in the presence of parts Circosol 42-40 and 2 parts of silane A174, as processing aids. The addition of the oil and sheeting out required about 5 minutes of milling time, compared to 10-15 min. where all ingredients were incorporated on the mill.

The physical properties of the SBR vulcanizates were:

A similar lignin-latex coprecipitate containing the ingredients (B) was made as in example 20, but in the absence of N" grade sodium silicate. The material was dried at 160F. About 133 g. of this material was macerated by means of a Waring hlcndor. then sheetcd as above with 5 parts Circosol 42-40 oil, but without the silane. The physical properties of the SBR vulcanizate were:

TABLE XVl Cure Time Modulus T (psi) 5,, H

at 275F (300% 35 min. 625 3280 810 72 40 min. 720 3600 780 75 The lignin-rubber from Example 21, can be molded into light-colored reinforced rubber products.

The lignin products of this invention would give beneficial properties when incorporated as a reactive reinforcing filler in the preparation of phenol-, or ureaformaldehyde resins, or in other plastics.

This invention envisages in practice the use of less water than prior examples have indicated. Water conservation can be realized through counter-current washing steps on the precipitated lignin, using wash water in the preliminary laundering step, and other regenerating and recycling procedures obvious to those skilled in the art.

EXAMPLE 22 About 200 g. crude lignin were soaked for 24 hours in 3 1. water containing 5 g. NaCl and 14 ml. 20 percent H 50 The suspension at about pH 2.5 was filtered. The residue was dispersed in about 8 l. of water at 61C and filtered. The filter cake was rinsed 5 times with 1 l. of water each time. The filter cake was dissolved in about 8 l. of water in the presence of 16 percent N grade sodium silicate with about 10 percent NaOl-l based on the weight of the original lignin, and precipitated at 92C with dilute hydrochloric acid. The suspension at about pH 3 was filtered immediately. The filter cake was rinsed 5 times with l l. of water each time. The wet lignin was dried at F overnight.

The physical properties of the vulcanizate filled with 40 parts lignin phr are:

TABLE XVll Modulus at 300% T, E, H

EXAMPLE 23 TABLE XVlll Modulus at 300% T E We claim: r .7,

l. A method of preparing a purified amorphous highly reinforcing lignin from impure crude lignin obtained directly from wood pulping liquors comprising;

a. laundering said impure crude lignin in an aqueous medium at a pH below about 6 until substantial amounts of non-lignin material are solubilized and separated, at water temperatures insufficient to degrade the lignin and below about 95C,

b. reforming the lignin by one of (i) precipitating with acid at a pH of about 2 to about 3 at a temperature of about 88 to 95C; and (ii) soaking wet lignin precipitate at said pH and said temperature, and

c. washing the precipitate to remove soluble material and drying the resulting solids.

2. The method of claim 1 wherein crude lignin separated from residual wood pulp liquors is dispersed in an aqueous laundering medium, soaked, filtered, and the lignin solids redispersed or dissolved in water or aqueous alkali before step (b).

3. The method of claim 1 wherein crude lignin is recovered from black liquor by centrifuging-off insolubles, heating the solution and lowering the pH until the lignin precipitates, cooling, filtering andwashing the lignin precipitate.

4. The method of claim 1, wherein as an aid in laundering one of the following additives is used: polar organic emulsifiers and bicarbonate salts.

5. The method of claim 1, wherein the laundering is effected at a pH of about 2-3.

6. The method of claim 3 wherein sodium chloride or sodium sulfate is added to the black liquor to aid in recovery of the lignin.

7. The method of claim 1, wherein before precipitation (b) (i), one of the following alkaline salts is present in the solution: sodium silicate, sodium borate and trisodium phosphate.

8. The method of claim 1, wherein before step (b) the lignin has been previously precipitated hot, filtered, washed and redissolved or redispersed.

9. The method of claim 1, wherein said crude lignin has been initially recovered by heating the crude pulp liquor to about 80-92C, centrifuging, reheating to said temperature and precipitating the lignin.

10. The method of claim 1, wherein a polar organic emulsifier selected from acetone, lower alkanols and triethanolamine is used as a laundering aid.

11. A laundered reformed highly amorphous lignin substantially free of non-lignin materials present in residual wood pulp liquors, having a surface area of from about 36 to about 52 M g, and reinforcing rubber (T to at least of the order of 2,800 p.s.i. as prepared by the method of claim I. 

2. The method of claim 1 wherein crude lignin separated from residual wood pulp liquors is dispersed in an aqueous laundering medium, soaked, filtered, and the lignin solids redispersed or dissolved in water or aqueous alkali before step (b).
 3. The method of claim 1 wherein crude lignin is recovered from black liquor by centrifuging off insolubles, heating the solution and lowering the pH until the lignin precipitates, cooling, filtering and washing the lignin precipitate.
 4. The method of claim 1, wherein as an aid in laundering one of the following additives is used: polar organic emulsifiers and bicarbonate salts.
 5. The method of claim 1, wherein the laundering is effected at a pH of about 2-3.
 6. The method of claim 3 wherein sodium chloride or sodium sulfate is added to the black liquor to aid in recovery of the lignin.
 7. The method of claim 1, wherein before precipitation (b) (i), one of the following alkaline salts is present in the solution: sodium silicate, sodium borate and trisodium phosphate.
 8. The method of claim 1, wherein before step (b) the lignin has been previously precipitated hot, filtered, washed and redissolved or redispersed.
 9. The method of claim 1, wherein said crude lignin has been initially recovered by heating the crude pulp liquor to about 80*-92*C, centrifuging, reheating to said temperature and precipitating the lignin.
 10. The method of claim 1, wherein a polar organic emulsifier selected from acetone, lower alkanols and triethanolamine is used as a laundering aid.
 11. A laundered reformed highly amorphous lignin substantially free of non-lignin materials present in residual wood pulp liquors, having a surface area of from about 36 to about 52 M2/g, and reinforcing rubber (TB) to at least of the order of 2,800 p.s.i. as prepared by the method of claim
 1. 